Electrical connectors providing electrical connections with one or several coaxial cables generally consist of an inner conductor, an insulating layer around the latter, a shield surrounding the insulating layer, generally in the form of a braided tube and a jacket around the shield. The contact element chambers of the connector housing accommodate contact elements, the inner conductors and the shields of the coaxial cables being connected with different contact elements. Each coaxial cable is assigned a pair of adjacent contact element chambers. Two-pin connectors of this type are of rectangular shape and take up two adjacent contact element chambers. Four-pin connectors are mostly of square external cross-section and accommodate two pairs of contact element chambers. Each pair of these contact element chambers accommodates an inner conductor contact element and a corresponding shield contact element. To provide a connection between the contact elements on the one hand and, the inner conductor and the shield on the other, the insulating jacket of the cable assembly is removed from the end which is to be connected with the connector. Subsequently the shield is bent away from the insulating layer surrounding the inner conductor and is connected with the corresponding contact element.
The areas where inner conductor and shield are separated, lie exposed outside of the connector housing. In order to electrically insulate the exposed shield conductors from each other and from external conductors and to stress-relieve the ends of the cable conductors in the connector housing, the cable inlet end of the housing connected with the coaxial cables in state of the art connectors is closed off by means of a casting compound, such as a polyacrylic adhesive. This is effected in such a way that the casting compound covers the housing from the cable inlet side to the area of separation of shield and inner conductor in a convex shape.
Plug-type connectors of this kind are mostly used in telecommunications, in particular for telephone systems. The matching contacts of such plug-type connectors are connection pins mounted on circuit boards. With modern technology, the packing density of connector pins on circuit boards has become very high, the dimensions of the connectors are correspondingly small.
The contact elements are equipped with locking springs which diagonally protrude from the contact elements towards the cable connection ends. Their free ends engage behind locking shoulders formed by recesses in the corresponding inner side walls of the contact element chambers. A contact element can only be pulled out of its contact element chamber by overcoming the locking force of the locking spring. Locking is only possible when the contact element is inserted into the contact element chamber in the correct turning position relative to its vertical axis.
Since the contact elements and consequently also the locking springs are rather tiny due to the small dimensions of such plug-type connectors, it is normally not sufficient to secure the contact elements in their chambers by means of locking springs. Therefore stress is additionally relieved by casting material around the cable inlet end of the connector.
From DE-PS 21 13 365 a connector housing of the afore-mentioned kind is shown where a number of contact elements are arranged in series next to each other. A flap is connected by means of a film hinge in transverse direction to the contact element row to a wall of the connector housing in such a way that in closed position it constitutes an extension of this wall. On the inside of the flap, there are perpendicularly protruding locking ribs which engage behind each contact element in the connector housing when the flap is closed and which release the contact elements when the flap is open. Therefore the contact elements can be inserted into their chambers or taken out of the latter without problems when the flap is open. When the flap is closed, the locking ribs secure the contact elements in the housing so that they cannot be torn out of the cable inlet end of the housing. The flap can engage with the rest of the housing by means of an engaging mechanism when it is closed.
The existing connector housing is open at the cable inlet side even when the flap is closed. The locking function of the locking ribs at the flap requires that the contact elements that are inserted into the connector housing are equipped with shoulders behind which an engaging mechanism may engage.
For multi-pin plug-type connectors with two rows of superimposed contact elements, it is only the row of contact elements next to the flap which can be secured by the locking ribs of this flap. If the top row of contact elements is also to be secured so that it cannot be drawn out of the cable inlet of the connector, there are plug-type connectors facing two vertical sides which are equipped with a flap each containing locking ribs. In other words, two rows of contact elements can only be secured by means of two flaps with locking ribs.
When the contact elements are mounted in the state of the art connector housing, each contact element, which has been adapted in shape to the locking mechanism, must be in its correct turning position about the vertical axis, otherwise the locking mechanism will fail. This exact positioning of the connector housing requires a lot of care and thoroughness of work by the assembly personnel or a highly sophisticated construction of the assembly machines.
U.S. Pat. No. 3,293,591 describes a two-pin connector the housing of which is open at the cable inlet end so that pin-shaped contact elements which are connected with the free ends of two electrical cables can be pushed through a common contact element cavity into an outlet opening at the plug-in side of the connector housing. In this case the cables connected with the contact elements at first protrude from the opening at the back of the connector housing. At a narrow side wall of the connector housing there is a cover which is attached to the housing by means of a film hinge. After the contact elements have been mounted in the housing, the cover is closed by a swivelling movement. This forces the cable ends connected with the contact elements into a recess in a vertical wall of the connector housing opposite the film hinge so that they are vertically guided out of the connector housing after the cover has been closed. The inside of the cover is provided with a clamping rib by means of which the cable sections guided out of the contact elements can be held stationary in the connector housing.
This clamping mechanism may be adequate for conductors which exclusively serve to conduct electrical energy. Problems arise, however, with signal transmitting cables. Coaxial cables which are connected to connectors for the above-mentioned telephone systems are geometrically deformed when squeezed in order to relieve stress. This changes the electrical characteristics of the cable and entails an undesirable change of the wave transmitting resistance of the cable.